The present invention relates to a process for manufacturing a semiconductor device having a glass coating on the surface of a p-n junction formed in a semiconductor body of the device, and more particularly to a process for manufacturing a semiconductor device with improved reverse characteristics.
It is well known in the art that in order to perform a high speed switching operation of semiconductor devices such as diodes, transistors, and thyristors, carrier life time of the devices must be made small and that the life time can be shortened by forming recombination centers in semiconductor bodies of the devices. The recombination centers are formed by doping heavy metal atoms such as gold in the bodies or by irradiating the semiconductor bodies with radiation rays or beams to cause lattice defects therein. Since the irradiation method as disclosed in U.S. Pat. Nos. 3,852,612; 3,888,701; 3,809,582, and 3,872,493 has a number of advantages over the doping method, there is a tendency to increase the use of the former method.
On the other hand, the demand for semiconductor devices having high blocking voltages and reliability is increasing, and to this end, the surface of a p-n junction exposed to the surface of a semiconductor body is often passivated by alkali-free glass as disclosed in U.S. Pat. Nos. 3,486,871; 3,551,171; 3,778,242; 3,650,778; 3,752,701; 3,505,571; and 3,674,520. According to experiments by the inventors, it has been revealed that when semiconductor devices passivated by the glass are irradiated by an electron beam, the reverse leakage current of the p-n junction with the glass layer increases remarkably, while there has been observed only a moderate increase in the leakage current when the surface is passivated by resins or varnishes. Because of the increase in the reverse leakage current, heat generation in the blocked state of the device makes it difficult to keep the blocked state and brings about such inconveniences as an increase in the power loss and malfunctions of the devices as well.